Polyorganosiloxanes are molecules made up of combinations of M, D, T, and/or Q units. M units have formula R′3SiO1/2, D units have formula R′2SiO2/2, T units have formula R′SiO3/2, and Q units have formula SiO4/2, where each R′ is monovalent and may be independently selected from organic and inorganic moieties. Generally, silicone resins are polyorganosiloxanes in which at least 30 mol % of the units in the molecule are T and/or Q units. MQ-type silicone resins (MQ resins) are polyorganosiloxane resins made up primarily of M and Q units. When MQ resins are produced, they typically contain 1% to 20% of groups of formula (RO), where R is a hydrogen atom or an alkyl group of 1 to 4 carbon atoms.
Capping is a process used to reduce the (RO) group content of the MQ resins, particularly when at least some of the R moieties are hydrogen atoms. Capped MQ resins, which have alkenyl groups bonded to silicon atoms in the M units, such as vinyl-functional MQ resins, are useful in compositions that can be cured by hydrosilylation and/or radical cure mechanisms. Such MQ resins find use in many industries and applications, such as additives for automotive airbag coating compositions. Current processes for capping MQ resins to reduce (RO) group content are time consuming and inefficient. There is an industry need to speed the reaction for producing such capped MQ resins.